Magnetic flux tubes inside the sun

Bipolar magnetic active regions are the largest concentrations of magnetic flux on the Sun. In this paper, the properties of active regions are invest igated in terms of the dynamics of magnetic flux tubes which emerge from th e base of the solar convection zone, where the solar cycle dynamo is believ ed to operate, to the photosphere. Flux tube dynamics are computed with the "thin flux tube" approximation, and by using magnetohydrodynamics simulati on. Simulations of active region emergence and evolution, when compared wit h the known observed properties of active regions, have yielded the followi ng results: (1) The magnetic field at the base of the convection zone is co nfined to an approximately toroidal geometry with a field strength in the r ange 3-10 x 10(4) G. The latitude distribution of the toroidal field at the base of the convection zone is more or less mirrored by the observed activ e latitudes; there is not a large poleward drift of active regions as they emerge. The time scale for emergence of an active region from the base of t he convection zone to the surface is typically 2-4 months. (2) The tilt of active regions is due primarily to the Coriolis force acting to twist the d iverging flows of the rising flux loops. The dispersion in tilts is caused primarily by the buffeting of flux tubes by convective motions as they rise through the interior. (3) Coriolis forces also bend active region flux tub e shapes toward the following (i.e., antirotational) direction, resulting i n a steeper leg on the following side as compared to the leading side of an active region. When the active region emerges through the photosphere, thi s results in a more rapid separation of the leading spots away from the mag netic neutral line as compared to the following spots. This bending motion also results in the neutral line being closer to the following magnetic pol arity. (4) The properties of the strongly sheared, flare productive delta-s pot active regions can be accounted for by the dynamics of highly twisted O mega loops that succumb to the helical kink instability as they emerge thro ugh the solar interior. (C) 2000 American Institute of Physics. [S1070-664X (00)97305-1].